In the field of 3-dimensional (3D) stacking of system-in-package (SiP) devices, packages are used with solder ball connections BGA (Ball Grid Array) and CSP (Chip Scale Package) style connections. Also in other fields, solder balls can be used to provide bonding between two elements.
In order to realize a dense 3D interconnection between such devices, small diameter solder-balls are required. However the diameter has to be larger than the height of the components, which are typically present on the individual SiP layers or elements.
Current RF wireless devices suffer from a large total module thickness or area because of the integration methods used to avoid coupling with the circuits while realizing enough antenna performance (bandwidth, efficiency).
One such device has an integrated antenna placed above circuit. A shielding layer is placed to avoid unwanted coupling between antenna and circuit. The shielding ground plane is part of the integrated antenna. A problem for such a wireless RF device is the thickness of the build-up. The antenna substrate thickness T should be typically larger then 4% of the free space wavelength to obtain enough antenna bandwidth and efficiency, i.e., the antenna substrate alone is several mm's to cm's thick for applications below 10 GHz. The antenna performance (bandwidth and efficiency) can only significantly be improved by increasing the distance between the antenna and the shielding ground plane layer.
Another such device has an integrated antenna placed next to a circuit (e.g., used in several commercial mobile devices including GSM, WLAN cards, etc.). The spacing S between antenna and circuit should be large enough to avoid influence between antenna and circuits. The (shielded) circuits are not considered as part of the antenna structure. A problem for this type of wireless RF device is the area of the build-up. Enough empty space (typically one quarter to half the free space wavelength) should be foreseen between antenna and circuits since the antenna performance can be influenced by the placement of nearby circuit and shielding elements.